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An Introduction to Collections
GemStone Programming Guide
Enumerating
Collection defines several methods that enable you to loop through a collection’s
elements. Because iterating or enumerating the elements of a data structure is one
of the most common programming tasks, Collection’s built-in enumeration
facilities are extremely useful; they relieve you of worrying about data structure
size and loop indexes. And because they have been carefully tailored to each of
Collection’s specialized subclasses, you needn’t create a custom iterative control
structure for each enumeration problem.
The most general enumeration message is do: aBlock. When you send a Collection
this message, the receiver evaluates the block repeatedly, using each of its
elements in turn as the block’s argument.
Suppose that you made an instance of IdentitySet in this way:
Example 4.4
| virtues |
virtues := IdentitySet new.
virtues addAll: #(’humility’ ’generosity’ ’veracity’
’continence’ ’patience’).
((UserGlobals at: #Virtues put: virtues) sortAscending: '')
verifyElementsIn: #[ 'continence', 'generosity',
'humility', 'patience', 'veracity' ]
To create a single String to which each virtue has been appended, you could use
the message do: aBlock like this:
Example 4.5
| aString |
aString := String new. "Make a new, empty String."
"Append a virtue, followed by a space, to the new String"
(Virtues sortAscending: '')
do: [:aVirtue | aString := aString , ' ' , aVirtue].
^ aString
continence generosity humility patience veracity
In this example, the method for do: executes the body of the block (aString ,
’ ’ , aVirtue) repeatedly, substituting each of Virtues’ elements in turn for the
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GemStone Systems, Inc.
December 2001